Summary of Research Programs
Wei Zhang, Ph.D.
Department of Pathology
The University of Texas MD Anderson Cancer Center
Published Scientific Accomplishments
Wei Zhang, Ph.D., and his research team are currently focused on two major areas: cancer genomics by gene and protein expression profiling, and functional regulation of tumor suppressor p53 by phosphorylation.
Dr. Zhang identified the first temperature-sensitive mutant of human p53 (EMBO J 13:2535-2544, 1994), illustrated the importance of functional analysis of p53 mutants found in human tumors by demonstrating that some p53 mutants only partially lose the DNA binding and transactivation functions (Oncogene 8:2555-2559, 1993; Cancer Res. 83:4772-4775, 1993), discovered that phosphorylation of p53 modulate the functions of p53 (Cancer Res. 54:4448-4453, 1994; Cell Death & Differentiation, 5:584-591, 1998) and identified that cell death promoting gene Fas/APO-1 and oncogene H-ras are transcriptionally regulated by p53 (Mol Cell Biol. 15:3032-3040, 1995; Int. J. Oncol 7:1021-1028, 1995).
He received NIH funding to further study the role of phosphorylation in functional regulation of p53, especially in response to radiation and chemotherapy treatment. In addition, he provided the first evidence that links the cell cycle regulator p21/WAF1/Cip1 to chemoresistance (Clin Cancer Res. 1:1051-1057, 1995), de-linked p21/WAF1/Cip1 from apoptosis promotion (Oncogene 11:2311-2316, 1995), identified p53-independent pathway for p21/WAF1/Cip1 activation (Cancer Res. 55:668-674, 1995; Cell Growth and Differentiation 6:909-913, 1995; Cancer Res. 57:3929-3934, 1997) and found that p21/WAF1/Cip1 is overexpressed in gliomas and brain metastases (Oncogene 11:2021-2028, 1995; J. Neuro-Oncol, 37:223-228, 1998).
Using a tetracycline-inducible system, he discovered that overexpressed p21/WAF1/Cip1 confers glioma cells resistance to BCNU and cisplatin (Cancer Res. 58:1538-1543, 1998). Using antisense approach, his group found that downregulation of p21/WAF1/Cip1 sensitized glioma cells to BCNU and cisplatin (Clinical Cancer Res. 5:197-202, 1999).
Dr. Zhang has been working on a glioma gene expression profiling program (J. Genetic Medicine 1:57-59, 1997; Oncol. Rep. 6:393-401, 1999; Oncogene 18:2711-2717, 1999; Cancer Res. 59:4228-4332, 1999) in collaboration with Drs. Fuller, Bruner, Yung and Hess. Profiles of 588 genes for over thirty glioma patients have been accumulated and several potential targets associated with a specific type of subgroup or a progression stage have been identified. A series of statistical analysis methodologies, such as hierarchical clustering analysis, multidimensional scaling and principal components analysis, has been used to analyze the profiling data. Some of these results have been submitted for publication.
Project 1: Gene Expression Profiling of Cancer
The goal of this program is to systematically profile gene expression patterns in cells derived from cancer patients using cDNA expression array and SAGE technologies. The ongoing projects include glioma studies. We anticipate that this systematic approach will yield information that will help us understand the molecular basis of gliomas and assays that will help future diagnosis of subsets of brain tumors. This project is a collaboration with neuropathologists Dr. Fuller and Dr. Bruner, neuro-oncologist Dr. Yung and statistician Dr. Hess. New collaborations with many investigators are under development in the areas of soft tissue sarcoma, colon cancer, bladder cancer, ovarian cancer, lymphoma and cancer metastases.
Project 2: Functional Characterization of IGFBP2 Pathway by Transgenic Model
In our recent publication in Cancer Research, we reported the overexpression IGFBP2 in GBM. In collaboration with Dr. Eric Holland, we will functionally test the role of IGFBP2 in gliomagenesis using a glial cell specific transgenic mouse model.
Project 3: Functional Regulation of p53 by Phosphorylation
Background. Homeostasis is maintained by coordinated cell death and cell proliferation. Abnormally blocked cell death and/or uncontrolled cell proliferation are two hallmarks of cancer. An important regulator of both cell death and cell proliferation is the tumor suppressor gene p53. Loss of one allele and acquisition of missense mutations in the remaining allele of p53 are frequent occurrences in human cancers (Hollstein 1991; Levine 1991). Functional loss of p53 normal alleles leads to increased proliferation and genetic instability, which is manifested by an accumulation of genetic changes such as point mutations, chromosomal rearrangement and gene amplification (Bischoff, F. 1990; Livingstone 1992; Yin 1992).
These accumulated genetic changes result in cellular immortalization and tumorigenicity (Vogelstein 1988; Weinberg 1989). It has been shown that overexpression of the p53 gene derived from a transfected expression vector or in response to radiation and DNA-damaging drugs may result in apoptosis in some tumor cells (Yonish-Rouach 1991; Shaw 1992; Clarke 1993; Lowe and Ruley 1993; Lowe 1993) and in proliferation inhibition in a wide spectrum of tumor cell types (Eliyahu 1989; Finlay 1989; Baker 1990; Mercer 1990). Accumulating evidence suggests that p53 protein governs cellular activities through the regulation of downstream genes that control different pathways (Kastan 1992; Kuerbitz 1992; Barak 1993; El-Deiry 1993; Owen-Schaub 1995). It has also been demonstrated that p53 activates expression of the Bax gene and inhibits expression of the Bcl-2 gene through specific DNA-responsive elements (Mishiyuki and Reed 1995; Miyashita 1994; Selvakumaran 1994; Zhan 1994). Our recent studies showed that p53 transcriptionally activates the expression of Fas/APO-1 (Owen-Schaub 1995). Wild-type p53 also transcriptionally activates the p21WAF1/Cip1 (p21) gene by interaction with two p53-binding enhancer elements on the promoter of the p21 gene (El-Deiry 1993).
All of these four genes (Bax, Bcl-2, Fas/APO-1 and p21) have been implicated in the control of apoptosis and the p21 gene in the inhibition of cellular proliferation (El-Deiry 1993; Zhang 1995). p53 also activates the expression of the DNA damage-inducible gene gadd45. A failure or a delay of p53 induction may in turn cause failure of gadd45 gene activation, which may be responsible for the radiation sensitivity of patients with ataxia-telangiectasia (Kastan 1992). Another p53-activated cellular gene is
In contrast, okadaic acid-induced phosphorylation decreases the transcriptional activation function of p53 based on a reporter gene assay (Zhang 1994). It is clear that phosphorylation at certain sites inactivates the functions of p53. In addition, the replacement of Ser 315 with Ala in human p53 does not affect its suppression function (Slingerland 1993). A mutation at the corresponding Ser 312 of mouse p53 does not abolish its ability to inhibit SV40- DNA replication (Meek and Eckhart 1990). Apparently, phosphorylation appears to modulate the function of p53 in a codon-specific manner. However, the information on this topic, especially the role of p53 phosphorylation in regulation of apoptosis, is very limited.
Specific Project. Our preliminary studies showed that radiation exposure caused the wild-type p53-containing leukemia cell line BV173 to apoptose rapidly and that treatment with arabinosyl cytosine (ara-C) caused a relatively slow apoptosis. Analyses of gene expression in the treated cells revealed that radiation activated both Bax and Fas/APO-1 expression, whereas ara-C activated Bax but not Fas/APO-1 expression. Two-dimensional gel electrophoresis of immunoprecipitated, 35S-methionine-labeled p53 of the treated cells showed that p53 existed as different isoforms with distinct isoelectric points in radiated and ara-C-treated cells. Phosphorylation is a key form of posttranslational modification that alters the isoelectric points of proteins. Therefore, these results strongly suggest that phosphorylation may play an important role in regulating the transcriptional activation functions of p53 in response to radiation and ara-C and in conferring the functional switch in the 143Ala ts mutant.
We hypothesize that differential phosphorylation of p53 accounts for its different transcriptional activities in irradiated and ara-C-treated BV173 cells. In this study we hope to identify important phosphorylation sites on p53 and shed light on the role of phosphorylation in the regulation of the p53 functions. We are also collaborating with Dr. Peng Huang in the Department of Clinical Investigation to study the regulation of p53's exonuclease activity in cells before and after treatment with chemotherapeutic agents.
- Understand the pathways that p53 functions regulate in cells.
- Identify tumor or lineage markers which may benefit diagnosis.
Impact / Significance
All three projects deal with regulation of genes and gene products that are important for cellular homeostasis. Understanding in these areas may have impact on cancer diagnosis and cancer therapeutic intervention.
Zhang, W., X-Y. Guo, G.-Y. Hu, W.-B. Liu, J. W. Shay, A. B. Deisseroth. 1994. A Temperature Sensitive Mutant of human p53. EMBO J. 13:2535-2544.
Zhang, W., C. McClain, J-P Gau, X-Y. Guo, A. B. Deisseroth. 1994. Hyperphosphorylation of p53 by Okadaic Acid Attenuates its Transcriptional Activation Function. Cancer Res. 54:4448-4453.
Zhang, W., L. Grasso, C. D. McClain, A. M. Gambel, Y. Cha, S. Travali, A. B. Deisseroth, W. E. Mercer. 1995. p53-independent Induction of WAF1/Cip1 in human myeloid leukemia cells is correlated with growth arrest accompanying monocyte/macrophage differentiation. Cancer Res. 55:668-674.
Owen-Schaub, L.B., W. Zhang, J. Cusack, L.S. Angelo, T. Fujiwara, R. Radinsky, J.A. Roth, A. B. Deisseroth, E. Kruzel. 1995. Wild-type and a temperature-sensitive mutant of human p53 induce Fas/APO-1 expression. Mol Cell Biol 15:3032-3040.
Zhang, W., S. M. Kornblau, T. Kobayashi, C.D. McClain, A. Gambel, A. B. Deisseroth. 1995. High levels of constitutive WAF1/Cip1 protein are associated with chemoresistance in acute myelogenous leukemia. Clinical Cancer Research 1:1051-1057.
Kobayashi, T., Consoli, U., Andreeff, M., Shiku, H., Deisseroth, A.B., Zhang, W. 1995. Activation of WAF1/Cip1 by a temperature sensitive mutant of human p53 does not lead to apoptosis. Oncogene 11:2311-2316.
Jung, J.M., Bruner, J.M., Ruan, S.-B., Langford, L., Kyritsis, A.P., Kobayashi, T., Levin, V.A., Zhang, W. 1995. Increased levels of p21WAF1/Cip1 in human brain tumors. Oncogene 11:2021-2028.
Kobayashi, T., Ruan, S.B., Clodi, K., Kliche, K.O., Shiku, H., Andreeff, M., Zhang, W. Overexpression of bax gene sensitizes K562 erythroleukamia cells to apoptosis induced by selective chemotherapy agents. Oncogene 16:1587-1591, 1998.
Ruan, S.B., Okcu, M.F., Ren, J.P., Clodi, K., Andreeff, M., Chiao, P., Levin, V., Zhang, W. Overexpressed p21/WAF1/Cip1 renders glioblastoma cells resistant to chemotherapy agents BCNU and cisplatin. Cancer Res. 58:1538-1543, 1998.
Kobayashi, T., Ruan, S.-B., Jabbur, J., Consoli, U., Shiku, H., Owen-Schaub, L., Andreeff, M., Reed, J., Zhang, W. Differential p53 phosphorylation and activation of apoptosis-promoting genes Bax and Fas/APO-1 by irradiation and ara-C treatment. Cell Death and Differentiation 5:584-591,1998.
For recent publications, search PubMed using keywords 'Zhang W' and 'Houston'.